In the design of lighting systems of the type used for illuminating roadways, parking lights, warehouses and the like, a primary goal is to obtain uniform illumination of the area covered by each individual light fixture in the system to avoid bright spots and dark spots on the surface being illuminated. Furthermore, it is desirable to minimize, as much as possible, the total amount of energy consumed by a lighting system, since energy costs in recent years have skyrocketed. Because of the low energy consumption which they require, high intensity discharge (HID) lamps have found widespread acceptance in such commercial applications. HID lamps, however, produce relatively weak light patterns in planes including the axis of the lamp, and produce strong light patterns in planes perpendicular to the lamp axis. This results in a good inherent light distribution below and on opposite sides of the lamp, but weak distribution of light off the ends of the lamp. For maximizing light output, however, these lamps typically are mounted in planes horizontal to the plane of the surface to be illuminated.
When laying out a pattern of luminaires to illuminate an area, such as a parking lot or the like, the lighting engineer has a limited number of choices of light distributions which are effected by employing pole layouts in various patterns. For example, if the pole layout is in the form of squares, it is desirable to employ luminaires, each one of which produces a square pattern of light. In this way, the square patterns of light may be nested against each other to give complete coverage of the area to be lighted. In other situations where the layout of the light poles may be on a rectangular pattern, a rectangular pattern of light from the individual luminaires would be beneficial. Whenever a luminaire produces a pattern of light which does not fit the exact area to be lighted, a problem is created with spilled light, due to lighting unwanted areas, with consequent power wasteage, or portions of the area to be lighted may have inadequate illumination.
In the past, various attempts have been made to adjust the patterns of the light emanating from a luminaire by the provision of segmented adjustable reflector sections in the luminaire. A typical luminaire of this type used with an incandescent lamp, however, and not subject to the unique light dispersion characteristics of HID lamps, is disclosed in the patent to Tolbert, U.S. Pat. No, 3,213,271. This patent is directed to a luminaire used for lighting residential streets and includes a pair of compound curved reflector segments mounted on opposite sides of the bulb. These reflector segments each are individually adjustable by sliding them in grooves to effect both vertical orientation or tilting and horizontal positioning about the bulb. Thus, reflected light may be shifted within a limited range upwardly or downwardly to direct the beam of light in appropriate directions on a hilly road and also, to adjust the beam laterally to maximize the direction of the beam on a curve in the road when the light fixture is located at such a curve. The reflector segments of Tolbert, however, do not compensate for a reduction in inherent lamp intensity in one or more directions, since this problem does not exist with the incandescent bulb used in the Tolbert fixture and mounted as disclosed in the Tolbert patent.
Another luminaire with adjustable reflectors in it for the purpose of providing an asymmetrical illumination of the region beneath the fixture is disclosed in the patent to Mousset, U.S. Pat. No. 4,261,029. The fixture of the Mousset patent mounts a lamp in an eccentric position within the fixture and locates adjustable reflector elements on opposite sides of the light-producing planes of the lamp to direct the light from the fixture off to one side of the region located beneath the fixture. There is no attempt to compensate for reduced illumination from the lamp in any planes where such reduced illumination, if any, takes place.
Other attempts to provide varying illumination in the form of adjustable luminaires for changing the light emitting therefrom from a floodlight configuration to a spotlight configuration and vice-versa are disclosed in the patents to Gulliksen, U.S. Pat. No. 4,338,655, and Snaper, U.S. Pat. No. 3,628,852. The Gulliksen discloses a main reflector in conjunction with a number of fan-type interengaging reflector sections to accomplish this purpose. The light pattern produced, however, in all of the configurations of the reflector elements in the Gulliksen device is a circular pattern. The Snaper patent also is a spot/flood reflector which uses a deformable material for the reflector to vary the curvature of the reflector behind the bulb and to widen or narrow the open end of the reflector. Once again, a circular light pattern is produced in all of the different configurations of the reflector element of the Snaper luminaire.
It is desirable to provide a luminaire which is capable of producing generally rectangular or square patterns of light of uniform intensity in the area beneath the luminaire which, at the same time, utilizes HID lamps or the like for the inherent desirable characteristics associated with such lamps. Further, it is desirable to provide such a luminaire which compensates for the inherent reduction in lamp intensity along the direction of the axis of an HID lamp.